1. The Field of the Invention
Embodiments of the invention relate to zwitterionic copolymers. More particularly, embodiments of the invention relate to copolymers that include zwitterionic monomers and alkoxy acrylate monomers and methods of making and using the copolymers.
2. The Related Technology
Implantable medical devices, including stents, can be coated with polymers to give the implantable device beneficial properties when used in living tissue. Implant coatings, particularly stent coatings, typically need to simultaneously fulfill many criteria. Examples of desirable properties for implant coating properties include: adhesion to the implant (e.g. adhesion to stent struts) to prevent delamination; adequate elongation to accommodate implant deformation without buckling or cracking; sufficient hardness to withstand crimping operations without excessive damage; sterilizability; ability to control the release rate of a drug; biocompatibility including hemocompatibility and chronic vascular tissue compatibility; in the case of durable or permanent coatings, the polymer needs to be sufficiently biostable to avoid biocompatibility concerns; processability (e.g. production of stent coatings that are microns thick); reproducible and feasible polymer synthesis; and an adequately defined regulatory path.
Recently, polymers containing 2-(methacryloyloxyethyl)-2′-(trimethylammoniumethyl)phosphate (“phosphorylcholine” or “PC”) monomers have been developed and used on implant devices. PC containing polymers have been shown to have many beneficial properties. For example, PC containing polymers are typically sterilizable, biocompatible, made from commercially available reagents, have received regulatory approval for certain embodiments, and provide a controlled drug release rate for higher molecular weight drugs.
However, PC coatings for use on implantable devices still need improvements with regard to several properties. Specifically, existing PC copolymers lack adequate elongation properties, especially when dry. Elongation properties are needed in order to accommodate implant deformation without coating buckling or cracking. Furthermore, PC copolymers need improvements in polymer hardness such that they can withstand crimping operations without excessive damage. Finally, some existing PC containing polymers have poorly controlled drug release rates for lower molecular weight drugs, including corticosteroids.